Neuronal nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that are implicated in a wide range of physiological functions, pathological processes and pharmacological effects. These receptors are the initial targets of nicotine and play an essential role in the development of nicotine addiction. In addition, these receptors may also be involved in developments of other addictions and in certain CNS disorders, including schizophrenia. Efforts to develop drugs targeting nAChRs have focused mainly on the ability of ligands to activate nAChRs. We hypothesize that many of the in vivo effects of nicotine in the CNS are mediated mainly by the desensitization of neuronal nAChRs, predominantly the 04(32 nAChRs. Based on our studies of in vitro pharmacological properties of sazetidine-A, a novel ligand that selectively desensitizes a4p2 nAChRs, we further hypothesized that (1) a nicotinic ligand that selectively desensitizes a4(32 nAChRs in vitro will produce some of the important in vivo effects of nicotine;and (2) such selective desensitizers of a4p2 nAChRs are potential therapeutic agents to aid smoking cessation. Based on these hypotheses, we propose to develop novel nicotinic therapeutics based desensitization of nAChR, rather than on activation of them. In the Project 1, our objective is to use in vitro pharmacological methods to profile novel ligands. We propose four Specific Aims to accomplish the objective: Aim 1, study equilibrium binding properties of all new ligands;Aim 2, study functional properties of new ligands using 86Rb+ efflux assays;Aim 3, study functional properties of new ligands using whole-cell patch clamp techniques;and Aim 4, characterize the pharmacological mechanisms related to desensitization induced by the novel ligands. The Aims of the Project 1 are closely related to proposed research in Project 2 (studies in animal behavioral models) and Project 3 (medicinal chemistry and animal tests for acute toxicity). We hope the collaborated efforts of the three projects will lead to drug candidates for Investigative New Drug applications, which may be used for treating nicotine addiction.